A series of tetranuclear-cluster-containing complexes based on pendent-arm macrocyclic ligand and different carboxylates: syntheses, structures, photoluminescence, and magnetic properties

Abstract

Eight new tetranuclear-cluster-containing compounds based on the carboxylate armed aza-macrocycle ligand, namely, [Co₄(L)(Ac)₂(H₂O)₄] (1), [Mn₄(L)(Ac)₂(H₂O)₄] (2), [Co₈(L)₂(L¹)₂(H₂O)₆]·H₂O (3), [Zn₈(L)₂(L¹)₂(H₂O)₆]·H₂O (4), [Co₄(L)(L²)(H₂O)₂]·H₂O (5), [Zn₄(L)(L²)(H₂O)₂]·H₂O (6), [Co₄(L)(L³)(H₂O)₄]·H₂O (7), and [Co₂(L)_0.5(L⁴)_0.5(H₂O)]·0.7H₂O (8), where HAc = acetic acid, H₆L = tetraacetic acid tetraaminodiphenol macrocyclic ligand, H₂L¹ = 1,3-benzenedicarboxylic acid, H₂L² = oxalic acid, H₂L³ = fumaric acid and H₂L⁴ = 1,6-hexanedioic acid, have been synthesized under hydrothermal conditions. Their structures have been determined by single-crystal X-ray diffraction analyses and further characterized by elemental analyses, IR spectra and thermogravimetric analyses (TGA). Compounds 1 and 2 possess the isostructural tetranuclear structures, which are further extended into 2D supramolecular layers via intermolecular O–H⋯O_carboxylate interactions. Compound 4 is isostructural with compound 3. In compound 3, the L¹ anions linked the tetranuclear cobalt–oxygen clusters to form a chain structure. The chains are further connected by intermolecular O–H⋯O_carboxylate hydrogen bonds to result in a 1D supramolecular double chain. Compounds 5 and 6 are isomorphous. Both 5 and 6 contain tetranuclear metal clusters. The tetranuclear metal clusters are bridged by L² anions to yield infinite chain structures. Compound 7 displays an infinite chain structure based on tetranuclear cobalt–oxygen clusters. The neighboring chains are further extended into a 2D supramolecular sheet by intermolecular O–H⋯O_carboxylate hydrogen bonds. Compound 8 shows a 1D zigzag chain structure constructed by tetranuclear cobalt–oxygen clusters and L⁴ anions. The variable-temperature (4–300 K) magnetic susceptibilities indicate that the tetranuclear metal unit in 2 exhibits antiferromagnetic as well as weak ferromagnetic exchange interactions, whereas in 1, 5, and 7 the exchange interactions are antiferromagnetic. Furthermore, the luminescent properties for compounds 4 and 6 have also been investigated.